Wednesday, February 3, 2010

Hello, Haplocheirus

There is a whole lot of dinosaur news going on right now. Predictably, the dinosaur feather color story has made the biggest splash in the general media. But there have also been two new species described in the last week or so.

Here's that new alvarezsaur I posted about last week. It's called Haplocheirus sollers, a basal member of the group, and the only one known from the Jurassic period. The discovery of Haplocheirus is one of those lovely instances when scientists make a prediction about evolution and it pans out. Many features of Haplocheirus are transitional between the later, more specialized alvarezsaurids and their common theropod ancestor. And it was found exactly where an early member of the group should be expected - in Jurassic rock dating to when theropods were diversifying into their myriad Cretaceous forms.

The hand in particular is remarkable. When I was in high school, the cool program we all loved messing with in art class allowed us to morph two faces together, an effect used to great artistic success in Michael Jackson's "Black and White" video. Take a look at the theropod hand comparisons used by Jonah Choiniere, lead author of the Nature paper describing the find, in his latest guest post at Archosaur Musings. It's like he took the hands of Allosaurus and Shuvuuia and morphed them, and ended up with Haplocheirus. Maybe not exactly, but close. Haplo looks a lot like a generic theropod, showing that the things that made its later descendants look so birdish really were examples of convergent evolution - separate lines that arrive at similar bodily features because the pressures of natural selection happened to favor them. The deeply keeled sternums of alvarezsaurs and birds allow for powerful arm muscles - muscles that evolved for digging and flying, respectively. Imagine I'm writing "cool" several hundred times, so I don't have to do it.

Another new species is a tyrannosaur unearthed in New Mexico, Bistahieversor sealeyi. I'll post on this one tomorrow.